Hybrid power transmission cord

ABSTRACT

A heat-treated cord comprising a low modulus yarn core that is wrapped by a plurality of high modulus wrapping yarns that were heat-treated for a time at a temperature and under a load sufficient to provide a free shrinkage of at least 2½ percent and a shrinkage force of at least 3 pounds.

FIELD OF THE INVENTION

The present invention relates generally to a hybrid power transmissioncord for use in elastomeric articles such as endless power transmissionbelts.

BACKGROUND

Endless power transmission belts, popularly referred to as V-belts, arewidely used throughout industry and such belts often have aload-carrying cord formed from a plurality of twisted yarns.

Applicant has recognized a long-felt but unmet need in the industry fora power transmission belt having both high flex fatigue life and lowbelt growth over the life of the belt, especially in misaligned uses.

An exemplary prior art cord 10 from U.S. Pat. No. 4,343,343 is shown inFIG. 1. FIG. 1 shows a composite cord 10 which is utilized to reinforceelastomeric articles, such as tires. This composite cord 10 comprises acore 12 around which is spirally or helically wrapped one or more hightenacity substantially inextensible yarns 14. In FIG. 1, two such yarns14 are shown wrapped about the core 12. U.S. Pat. No. 4,343,343comprises an unoriented polymeric core with elongation at break of atleast 200%, which is very different from the present invention.

SUMMARY

A cord comprising a low modulus yarn core that is wrapped by a pluralityof high modulus yarns. This design is believed to provide good tensilestrength and flex fatigue life even in misaligned outdoor powerequipment uses.

An exemplary heat-treated hybrid cord comprises:

-   -   a. at least one core yarn having a Young's modulus; and    -   b. a plurality of wrapping yarns twisted around the at least one        core yarn, each wrapping yarn having a strength of at least 2.5        GPa and a Young's modulus that is at least 5 GPa greater than        the Young's modulus of the at least one core yarn; and    -   c. wherein the wrapping yarns are twisted in a first direction        and then twisted in the opposite direction in the range from        about 1 to about 7 twists per inch around the at least core yarn        to form a greige cord; and    -   d. wherein the wrapping yarns in the greige cord have an        untwisted yarn length that is about 0.8% to about 5% greater        than the untwisted yarn length of the at last one core yarn in        the greige cord; and    -   e. wherein after twisting the residual twist for the at least        one core yarn is in the range from about 1 to about 7 twists per        inch in the greige cord and after twisting the residual twist        for the wrapping yarns is in the range from about 2 to about 8        twists per inch in the greige cord; and    -   f. wherein the heat-treated hybrid cord has a LASE3 value of at        least 190 pounds and an elongation at break of less than 10%.

An exemplary endless power transmission belt comprises an elastomericbody and at least one heat-treated hybrid cord disclosed herein embeddedin the elastomeric body.

An exemplary method of making a heat-treated hybrid cord comprises:

-   -   providing at least one core yarn having a Young's modulus; and    -   providing a plurality of wrapping yarns, each wrapping yarn        having a strength of at least 2.5 GPa and a Young's modulus that        is at least 5 GPa greater than the Young's modulus of the at        least one core yarn; and    -   pre-twisting the wrapping yarns in a first direction with a        twist multiplier in the range of about 2 to about 6½; and    -   twisting the pre-twisted wrapping yarns and the core yarn in the        opposite direction with a twist multiplier in the range of about        2 to about 6½ to form a greige hybrid cord; and    -   then heat-treating the greige cord; and    -   wherein the wrapping yarns in the greige cord have an untwisted        yarn length that is about 0.8% to about 5% greater than the        untwisted yarn length of the at last one core yarn in the hybrid        cord.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows a prior art cord;

FIG. 2A is a photograph of a cross section of an exemplary cordaccording to the principles of the present application;

FIG. 2B is a schematic cross-sectional view of an exemplary cordaccording to the principles of the present application;

FIG. 3A is another schematic cross-sectional view of another exemplarycord that is annotated to illustrate an equation used to calculate themaximum number of wrapping yarns that can be included in a single layeraround a core yarn;

FIG. 3B provides additional context for the equation used to calculatethe maximum number of wrapping yarns that can be included in a singlelayer around a core yarn;

FIG. 4 defines the yarn length contraction “S” for twisting processes;

FIG. 5 is a schematic representation of a V-belt test configuration,which is used to test Flex Life and CD Change of V belts made with thecords of the present application;

FIG. 6 is a perspective cross-sectional view illustrating one exemplaryembodiment of an endless power transmission belt;

FIG. 7 is an enlarged transverse cross-sectional view taken along 2-2 ofFIG. 6;

FIG. 8 is a cross-sectional view of another exemplary embodiment of anendless power transmission belt;

FIG. 9 illustrates a partial cut-away of a belt building drum (mandrel)showing the different layered components assembled on the drum toconstruct a belt sleeve;

FIG. 10 is a transverse cross section of a multi-V-ribbed belt used inthe accessory drive system of taken along 2-2 of FIG. 11;

FIG. 11 is a simplified engine accessory drive system utilizing amulti-V-ribbed belt of FIG. 10;

FIGS. 12 and 13 are boxplots showing data from V belts made with ahybrid core in accordance with the present application.

DETAILED DESCRIPTION

The present application discloses a cord comprising a low modulus yarncore that is wrapped by a plurality of high modulus yarns (“hybridcord”). An exemplary cord consists of a low modulus polyester yarn corethat is wrapped by a plurality of high modulus aramid yarns. Anexemplary embodiment of this cord consists of a low modulus polyesteryarn core that is wrapped by a maximum number of high modulus aramidyarns. These cords are believed to provide good tensile strength andflex fatigue life even in misaligned uses, such as misaligned outdoorpower equipment uses.

As used herein, “denier” or “den” is a unit of measure for the linearmass density of fibers and is the mass in grams per 9,000 meters.

As used herein, a “low modulus” yarn means a yarn having a Young'smodulus of 5.0 to 70 gigapascals (GPa or kN/mm²).

As used herein, a “high modulus” yarn means a yarn having a Young'smodulus greater than 70 GPa and a strength greater than 2.5 GPa.

As used herein, “residual twist” means the twist remaining from thefirst twisting operation (or remaining from any intermediate twistingoperations) after the final twisting operation in the opposite directionand is an indicator of the force within a twisted yarn construction thatmakes it tend to wind or unwind itself after the twisting operation iscomplete.

As used herein, “twists per inch” or “turns per inch” or simply “tpi” isa measure of how much twist a yarn has and means literally the number oftwists in an inch of the yarn. It can be calculated in plied yarnscounting the number of humps in one inch of the yarn and dividing by thenumber of strands plied together to make the yarn.

As used herein, “twist multiplier” or “TM” means the ratio of turns perinch to the square root of the yarn count. The yarn count can beestimated by 5315/denier. Thus, in general, the twist multiplier can beestimated by using the following:TM=0.01372×(denier)^(1/2)×tpi(from Wellington Sears Handbook of Industrial Textiles, Sabit Adanur,Technomic Publishing Co., 1995, page 616).

Referring now to the figures, FIGS. 2A and 2B show cross sections of anexemplary cord 20 according to the principles of the presentapplication. Exemplary cord 20 comprises a low modulus yarn core 22 thatis wrapped by a plurality of high modulus wrapping yarns 24. Thus, thelow modulus core is relatively flexible as compared to the high moduluswrapping yarns. Each of the yarns 22, 24 may be composed of a pluralityof filaments which are cabled together or twisted around each other.

The core 22 may consist of a yarn having a Young's modulus of 5.0 to 70gigapascals GPa. Polyesters and/or polyamides are suitable materials forthe core 22. Other suitable materials for the core 22 include PAN(polyacrylonitrile), PEN (polyethylene naphthalate), PTFE(polytetrafluoroethylene), PVDF (polyvinylidene fluoride orpolyvinylidene difluoride), FEP (Fluorinated ethylene propylene), PE(polyethylene, polythene, polyethene, or poly(methylene)), and PP(polypropylene). Exemplary embodiments of cores include (a) a 2000denier polyester core that has a radius of 0.011 inches, (b) a 3000denier polyester core that has a radius of 0.013 inches, and (c) a 4000denier polyester core that has a radius of 0.016 inches.

The wrapping yarns 24 may each consist of a yarn having a Young'smodulus greater than 70 GPa and a strength greater than 2.5 GPa. Aramidyarn is a suitable material for the wrapping yarns 24. Other suitablematerials for the wrapping yarns 24 include PBO (polybenzobisoxazole),glass, Vectran (an aromatic polyester produced by the polycondensationof 4-hydroxybenzoic acid and 6-hydroxynaphthalene-2-carboxylic acid),PIPD (poly diimidazo pyridinylene dihydroxy phenylene or M5), HPPE (highperformance polyethylene), and carbon fiber. Exemplary embodiments ofwrapping yarns include (a) a 1500 denier aramid yarn that has a radiusof 0.009 inches and (b) a 3000 denier aramid yarn that has a radius of0.013 inches. The aramid yarns may be TWARON brand aramid yarns.

Although the cord 20 is shown with five yarns 24 wrapping the core 22,other numbers of wrapping yarns can be used. To obtain the highestoverall cord strength for a given cord diameter, the maximum number ofwrapping yarns 24 that can be included in a single layer around the coreyarn 22 can be used. The maximum number of wrapping yarns 24 that can beincluded in a single layer around a core yarn 22 is given by thefollowing formula with reference to FIGS. 3A and 3B:Max Wrap Yarns=cos β·π/αwhere

-   -   β=tan⁻¹ (π·T·2·[r_(w)+r_(e)])    -   α=sin⁻¹(r_(w)/[r_(w)+r_(c)])    -   T=twists per inch    -   r_(c)=radius of core yarn    -   r_(w)=radius of wrapping yarn        For example, using a 2000 denier polyester core yarn, five 1500        denier aramid wrapping yarns, and a desired T of 4.1 twists per        inch,    -   r_(c)=0.011 in.    -   r_(w)=0.009 in.    -   T=4.1 twists per inch        β=tan⁻¹(π·T·2·[r _(w) +r _(c)])=27.3°=0.476 rad        α=sin⁻¹(r _(w) /[r _(w) +r _(c)])=26.7°=0.467 rad        and the maximum number of wrapping yarns that can be included in        a single layer around a core yarn in that example is given by        cos β·π/α=5.98; thus 5 is the maximum number of yarns that can        be wrapped around the selected core in this example.

Using a maximum number of high modulus wrapping yarns around a lowmodulus core allows breaking strength and modulus of the cord to beoptimized without increasing final cord diameter. If even higher tensilestrength is required, a larger core yarn may be used and thecorresponding maximum number of wrapping yarns may be increased.Increasing the denier of the wrapping yarns will also increase thetensile strength of the cord.

Twisting the Cord

A number of processes can be used to make cords comprising a low modulusyarn core that is wrapped by a plurality of high modulus yarns, e.g.,cords with aramid yarns wrapping a polyester core. Unlike other cords,yarn twist is selected without matching the moduli of the differentyarns.

Two exemplary twisting processes for twisting hybrid cords are set forthbelow:

Twisting Process 1

In a first exemplary process, a twister (such as a ring twister, a twofor one twister, or a flyer twister) is used to manufacture a fullytwisted greige cord. In a first stage the low modulus core yarn istwisted using a twist multiplier (TM) of 0 to 8 (calculated usingTM=0.01372·T·(denier)^(1/2), where T is the number of twists per inch).In a second stage, the high modulus wrap yarns are then twisted aroundthe core in the opposite direction (with respect to the first wrapping)and again using a TM of 0 to 8 (calculated the same way). The lengths ofthe wrap yarns to the core yarn are in the range of 0.5% to 5.0% (theuntwisted lengths of the wrap yarns are a little longer than theuntwisted length of the core yarn), which length difference is achievedby either one of the following two methods:

-   -   1. Creating a tension difference between the core and wrapping        yarns of 0.005 to 1.0 grams/denier during the second stage; or    -   2. Using a feed rate difference between the core yarn and the        wrapping yarns in the range of 0.5% to 5.0% during the second        stage.

In general, with Twisting Process 1, the wrapping yarns are pre-twistedwith a TM of 0.0 to 6.0, the core yarns are pre-twisted with a TM of 0.0to 6.0, and the final twist TM is 2.0 to 6.0 (using the Wellington Searscalculation method, set forth above).

Twisting Process 2

As seen in FIG. 4, when a yarn is twisted, its overall length decreasesby some amount S in the Z direction. Likewise when a twisted yarn isuntwisted its length increases by an amount S in the Z direction. Thiscan be used to make cords according to the present application.

In a second exemplary process, a twister (such as a ring twister, a twofor one twister, or a flyer twister) is used to manufacture a fullytwisted greige cord. Two types of yarns are twisted together on thetwister. The first yarn is the core, which has zero twist. The secondyarns are the wrapping yarns, which have a TM of 0 to 8 in either the Sor Z direction. Both yarns are twisted on the twister and combined witha TM of 0-8 in the opposite direction (with respect to the wrappingyarns). When the core yarn is twisted it shrinks as shown in FIG. 3C.When the wrapping yarns are twisted in the second or combining stage (inthe opposite twisting direction of the first stage) their lengthincreases. This combined yarn structure forces the wrapping yarns towrap around the core yarn because of their greater length. This combinedstructure keeps the core yarn at the core because of its shorter length.In this process the untwisted length of the core yarns to the wrappingyarns is 0.5 to 5.0%.

In general, with Twisting Process 2, the core is not pre-twisted, thewrapping yarns are pre-twisted with a TM of 2.0 to 6.0, and the finaltwist TM is 2.0 to 6.0 (using the Wellington Sears calculation method,set forth above).

After twisting (using either Twisting Process 1 or Twisting Process 2 orsome other process), the residual twist for the hybrid cords can be inthe range of from 1.0 to 7.0 twists per inch in the core yarn and2.0-8.0 twists per inch in the wrapping yarns. The final twistingprocess can be in the range of 1.0-7.0 twists per inch.

Cord Heat Treatment

After twisting the low modulus yarn core and the plurality of highmodulus wrapping yarns to form a greige cord (using either TwistingProcess 1 or Twisting Process 2 or some other process), the cord istreated by heating the greige cord under load to increase the Young'smodulus of the cord without significantly decreasing its breakingstrength. More specifically, the greige cord is loaded with about 0.1 toabout 3 grams per denier tension and heated at a temperature of about100° C. to about 235° C. for about 25 seconds to about 150 seconds in anoven, e.g., the greige cord is treated with the process conditionsoutlined for ES1551 or RF2161 or ES1549 in Table 5.

This Cord Heat Treatment allows the modulus of a hybrid cord to changeduring processing to approach the modulus of the 100% aramid material.Table A, below, shows the effect of the Cord Heat Treatment on a controlcord (Aramid 1500×2×3) and three hybrid cords:

TABLE A Greige Cord Breaking Total Free Shrinkage Strength ElongationLASE3 ID Description Denier Shrinkage % Force lb lb at Break lb RF2261Aramid 1500 × 2 × 3 9,000 — — 366.5 4.3% 200.6 ES1551 PET/Aramid Hybrid2000 PET core, 9,500 — — 353.3 5.1% 152.9 5 × 1500 Aramid wrap ES1549PET/Aramid Hybrid 4000 PET core, 13,000 — — 388.7 6.4% 96.0 6 × 1500Aramid wrap RF2161 PET/Aramid Hybrid 3000 PET core, 15,000 — — 422.46.5% 98.0 4 × 3000 Aramid wrap After Cord Treatment Breaking Total FreeShrinkage Strength Elongation LASE3 % Change ID Description DenierShrinkage % Force lb lb at Break lb LASE3 SC1119 Aramid 1500 × 2 × 39,000 — — 378.7 3.8% 289.8 44.5% ES1551 PET/Aramid Hybrid 2000 PET core,9,500 2.7% 3.0 325.5 3.8% 240.6 57.4% 5 × 1500 Aramid wrap ES1549PET/Aramid Hybrid 4000 PET core, 13,000 4.3% 4.4 406.0 5.2% 197.4 105.6%6 × 1500 Aramid wrap SC1223 PET/Aramid Hybrid 3000 PET core, 15,000 —16.0 419.8 4.3% 291.0 197.0% 4 × 3000 Aramid wrap

RF2261 is the identifier for the greige cord for the SC1119 hybrid cord.RF2161 is the identifier for the greige cord for the SC1223 hybrid cord.The “Aramid 1500×2×3” RF2261 control in Table A was made from 1500denier aramid base yarn and twisted as follows: 2 plies of 1500 denieryarn were twisted at 4.6 tpi in the Z direction and 3 strands of 1500×2yarn were twisted in a second twist operation with 4.6 tpi in the Sdirection.

In Table A, Total Denier is the denier for the cord (as a whole), FreeShrinkage is a length change measured by exposing untensioned cord for 3minutes at 175° C. in a hot air oven, Shrinkage Force is measured on aTestrite® tester by heating a cord at 110° C. for 2 minutes with apretension of 0.1 g per denier, Breaking Strength is the breakingstrength (in pounds) of the cord measured on an Instron® or MTS® tensiletester, and LASE3 is a measurement of load at 3 percent elongationmeasured on an Instron® or MTS® tensile tester. The LASE3 valuecorrelates to Young's modulus. The “Pet/Aramid Hybrid 2000 PET core,5×1500 Aramid Wrap” cord was made in accordance with the presentapplication using Twisting Process 2 on a 2000 denier polyester coreyarn and 5 each 1500 denier aramid wrap yarns (“hybrid cord”) andcorresponds to Example 1 (ES1551) below. Similarly, RF2161/SC1223corresponds to Example 2 and ES1549 corresponds to Example 3, below. A“-” in Table A indicates that the value was not measured.

As can be seen from Table A, after the cord heat treatment the breakingstrength of two of the hybrid cords dropped a little, but the Young'smodulus value (LASE3) of the hybrid cords increased significantly andactually increased more than the aramid control cord. Although notwanting to be bound by theory, it is believed that the Cord HeatTreatment affects the cord to achieve these positive effects by allowingthe lower modulus core yarns to stretch sufficiently for the highermodulus wrapping yarn modulus to become dominant, i.e., it is believedthat the Cord Heat Treatment permits the lower modulus core yarns tostretch in the range of 1.0 to 10.0% so that the higher modulus wrappingyarns carry a load proportional to their denier and modulus. The levelof elongation of the low modulus core of the hybrid yarns is seen in thedifference between the elongation at break, or failure strain, of thegreige cord and the after treatment cord.

EXAMPLES

Three exemplary cords, Examples 1-3, are shown in Table 1, below:

TABLE 1 Examples 1-3 Core Radius Wrap Radius # of Core Yarn Core WrapYarn Wrap Wrap yarn final Total Ex Material Denier (in) Material Denier(in) Yarns tpi tpi Denier 1 Polyester 2000 0.011 Twaron 1500 0.009 5 64.1 9500 ES1551 Aramid 2 Polyester 3000 0.013 Twaron 3000 0.016 4 4.43.4 15000 RF2161 Aramid 3 Polyester 4000 0.016 Twaron 1500 0.009 6 6 3.813000 ES1549 Aramid

In the exemplary cords of Examples 1-3, there is one (1) single coreyarn assembly wrapped by the indicated number of wrapping yarns. Thepolyester core yarn has a Young's modulus of about 14 GPA. The aramidwrapping yarns have a Young's modulus of about 74 GPa. The cords ofExamples 1-3 were twisted using Twisting Process 2. Example 1 (ES1551)has a residual twist in the wrapping yarns of 1.9 tpi Z, Example 2(RF2161) has a residual twist in the wrapping yarns of 1.0 tpi Z, andExample 3 (ES1549) has a residual twist in the wrapping yarns of 2.2 tpiZ.

Table 2 shows the various twist multipliers used in Examples 1-3:

TABLE 2 yarn tm final tm final tm Description Identifier yarn tm arafinal tm ara pet Thickness Aramid/Polyester Hybrid ES1551 3.19 3.42 5.485.88 5.47 0.047 Aramid/Polyester Hybrid RF2161 3.31 3.54 5.71 6.12 5.700.061 Aramid/Polyester Hybrid ES1549 3.19 3.42 5.94 6.37 5.94 0.056

In Table 2, “yarn tm” is the twist multiplier for the first twistingprocess of the aramid wrapping yarn using the formula,TM=0.01372×denier^(1/2)×tpi, “yarn tm ara” is the twist multiplier forthe aramid wrapping yarns using the formula, TM=tpi×denier^(1/2)/68,“final tm” is the final twist multiplier for the final twisted greigecord using the formula, TM=0.01372×denier^(1/2)×tpi, “final tm ara” isthe final twist multiplier of the final twisted greige cord using theformula, TM=tpi×denier^(1/2)/68, “final tm pet” is the final twistmultiplier of the final twisted greige cord using the formula,TM=tpi×denier^(1/2)/73, and “thickness” is the final thickness(diameter) of the greige cord in inches. This Table 2 shows there isvery little difference between the preferred formulaTM=0.01372×denier^(1/2)×tpi and the alternate formulas.

Table 3 shows the calculated maximum number of wrapping yarns that couldbe included in a single layer around the core yarn in Examples 1-3. Ascan be seen, Example 1 used the calculated maximum number of wrappingyarns that can be included in a single layer around the core yarn (fivewrapping yarns), but Examples 2 and 3 used one wrapping yarn fewer thanthe maximum number of wrapping yarns that could be included in a singlelayer around a core yarn (four wrapping yarns instead of five in Example2 and six instead of seven in Example 3).

TABLE 3 Number Of Max Max Warp Total Yarn Yarn Ex Identifier Yarns yarntpi final tpi Denier Beta Alpha Calculation Integer 1 ES1551 5 6 4.19500 0.476 0.467 5.983 5 2 RF2161 4 4.4 3.4 15000 0.510 0.507 5.404 5 3ES1549 6 6 3.8 13000 0.530 0.375 7.222 7

Table 4, below, shows the ply length difference between the wrap yarnsand the core yarn for Examples 1-3. In each example, the wrapping yarnsare slightly longer than the core yarn.

TABLE 4 Ply Length Difference Between Wrap Description ExampleIdentifier and Core Aramid/Polyester Hybrid 1 ES1551 0.87%Aramid/Polyester Hybrid 2 RF2161 2.32% Aramid/Polyester Hybrid 3 ES15492.03%

The cords of Examples 1-3 were heat treated using the Cord HeatTreatment discussed above with the tension (pounds), time (seconds), andtemperature (degrees F.) shown in Table 5, below:

TABLE 5 Zone 2 Zone 3 Zone 1 Zone 2 Zone 3 Identifier Ex Zone 1 Expos sZone 2 Expos s Zone 3 Expos s Zone 1 Temp F. Temp F. Temp F. TensionTension Tension ES1551 1 99 79 79 380 240 450 6 12 15 RF2161 2 111 87 66360 240 450 5 12 25 ES 1549 3 132 105 105 380 240 450 6 12 22

In Table 5, the different zones represent three independent hot airovens with capabilities to independently control cord tension in eachoven. Table 5 represents a three zone process for V Belt cords. Thefirst oven and tension zone (Zone 1) is used for the application andcuring of a first adhesive, typically epoxy or isocyanate. The secondoven and tension zone (Zone 2) is used for the application of aresorcinol formaldehyde latex (RFL) and the drying of that adhesive. Thethird oven and tension zone (Zone 3) is used to react the RFL adhesive.Heat treating temperatures and exposure are determined experimentally toachieve optimal adhesion of the cords to rubber. There is a directrelationship between third zone tension and shrinkage force. Load isselected to attain a desired level of shrinkage force. In theseexamples, a load during heat treatment in Zone 3 of about 0.7 to about0.8 grams per total greige cord denier was applied. The third zone (Zone3) exposure time, temperature, and tension are the primary factorsinfluencing the properties listed in Table 6, below.

The data shown above in Table 1 (Free Shrinkage %, Shrinkage Force lb,Breaking Strength lb, and LASE3 lb), indicating the effects of the heattreatment, are shown in Table 6, below, for all three Examples:

TABLE 6 Free Shrinkage Breaking LASE3 Identifier Ex Shrinkage % Force lbStrength lb lb ES1551 1 2.7 3.0 325.5 240.6 RF2161 2 — 16.0 419.8 291.0ES1549 3 4.3 4.4 406.0 197.4Belts Made with Hybrid Cords

The hybrid cords discussed above can be used in the manufacture ofelastomeric articles such as endless power transmission belts.

Reference is now made to FIGS. 6 and 7 of the drawings which illustratean exemplary embodiment of an endless power transmission belt structureor belt of this disclosure. The belt structure or belt is designatedgenerally by the reference numeral 100. Such belt 100 has trapezoidalcross-section and may often be referred to as a V-belt. The belt 100 hasa pair of opposed parallel surfaces, which when viewed in cross-section,are defined by an outside surface 101 and an inside surface 102 with theparallel surfaces 101 and 102 being connected at their opposite edges bysymmetrically arranged side surfaces 103. The side surfaces 103 definethe non-parallel sides of the trapezoidal cross-section of belt 100.

Belt 100 has a load-carrying section 104 arranged midway between theoutside surface 101 and the inside surface 102. Because the practice inthe industry is to refer to the load-carrying section 104 as the neutralaxis of the belt, the positioning of the load-carrying section 104midway between surfaces 101 and 102 results in what may be referred toas belt 100 having a central neutral axis. The belt 100 also includes atension section 105 and a compression section 106. The load-carryingsection 104 is disposed between tension section 105 and compressionsection 106.

The load-carrying section 104 has, as its load-carrying means, thecomparatively highly twisted helically wound load-carrying cord 20disclosed herein. In accordance with this embodiment, the belt 100containing cord 20 has improved performance, including but not limitedto improved resistance to flex induced fatigue failure (i.e., longerFlex Life) and lower degradation of tensile strength.

Cord 20 is suitably embedded in an elastomeric cushion 107 in accordancewith techniques known in the art. The cushion 107 comprises theload-carrying section 104. The cushion 107 may be made of any suitablematerial known in the art such as a soft rubber, for example.

The tension section 105 of the belt 100 has a fabric cover 108 thereon,the outside surface of which defines the outside surface 101 of the belt100. Similarly, the compression section 106 has a fabric cover 109thereon the outside surface of which defines the inside surface 102 ofthe belt 100. The covers 108 and 109 may be made employing any suitablefabric employed in the art of making belts.

Each of the sections 105 and 106 also has a plurality of fibers orientedparallel to surface 102 and perpendicular to cord 20 embedded therein, arepresentative few of which are designated by the reference numeral 110.The fibers 110 allow the belt 100 to be operated in its endless pathwith unimpaired longitudinal flexibility while providing transverserigidity or stiffness for such belt, i.e., stiffness transverse thelongitudinal axis of the belt. The fibers 110 may be made of anysuitable material known in the art.

Each of the sections 104, 105, and 106 of the belt 100 is preferablymade primarily of a polymeric material in the form of a rubber compoundwith the only exceptions being the fibers 110, fabric covers 108 and109, and the cord 20. Any suitable rubber or rubber compound disclosedherein may be used with the embodiments of the belts disclosed herein.

Another exemplary embodiment of the belt structure or belt of thisinvention is illustrated in FIG. 8 of the drawing. The belt illustratedin FIG. 8 is very similar to the belt 100; therefore, such belt isdesignated by the reference numeral 100A, and representative parts ofthe belt 100A that are similar to corresponding parts of the belt 100are designated in the drawing by the same reference numerals as in thebelt 100 (whether or not such representative parts are mentioned in thespecification) followed by the letter designation “A” and not describedagain in detail. Only those parts of the belt 100A which aresubstantially different from the belt 100 are designated by a newreference numeral, also followed by the letter designation “A” anddescribed in detail below.

The belt 100A of FIG. 8 has a tension section 105A, a load-carryingsection 104A, and a compression section 106A. A primary differencebetween belt 100A and belt 100 is that belt 100A has its load-carryingsection 104A disposed closer to its outside surface 101A than to itsinside surface 102A as compared to the load-carrying section 104 withrespect to the corresponding surfaces 101 and 102 in belt 100. The belt100A also has a fabric cover designated by the reference numeral 111Awhich extends completely around the periphery of the belt as shown inthe in cross-section of FIG. 8 and has an overlapping inside surface asindicated at 112A. This type of belt 100A may often be described as a“wrapped belt.” However, the belt 100A is not limited to wrapped beltsand instead may have raw-edged non-parallel sides in a similar manner asthe belt 100 described herein. Further, both exemplary belts 100 and100A may be raw-edged or without covers about their entire peripheries.

Referring first to FIGS. 10 and 11 of the drawings, in accordance withother exemplary embodiments, an engine accessory drive system is showngenerally at 150, consisting of an engine crankshaft pulley 154, and adriven pulley 152 linked in driving relationship by a four-ribbedserpentine belt 151 that contains the cords 20 disclosed herein. The topor exterior back surface 153 of belt 151 makes contact with idler pulley156. The drive system 150 of FIG. 11 may be used as a simple automotiveaccessory drive system, an industrial drive, or a test apparatus formeasuring noise generated at the interface between belt 151 and backsideidler pulley 156 through sensor/transducer 158 (measuring dB's(decibels) and noise characteristics). The particular application andtype of drive system will be dictated by the type of belt configurationchosen. Generally the cords of this disclosure may be applied toV-belts, flat belts, multi-V-ribbed belts and synchronous belts. Anexample of a common automotive front end accessory drive system in whichthe belt of the invention may be used is illustrated and disclosed inU.S. Pat. No. 4,551,120, which consists of a main driving pulleyoperatively connected to an air conditioning motor pulley, an alternatorpulley, an engine air pump pulley, and a water pump pulley. Themulti-V-ribbed belt trained about these pulleys is kept in appropriatetension through a tensioner having a surface engaging the backside ofthe belt.

The belt of FIG. 10 is formed of a rubber body. As used herein, “rubber”or a “rubber compound” refers to a cross-linkable natural or syntheticrubber which is processable in solid form, e.g., on a mixing mill. Suchrubber is typically mixed in a green or unvulcanized form withappropriate additives, extenders, reinforcements, accelerators, fillers,vulcanizing agents such as sulfur and peroxides, and the like in aBanbury® mixer, or continuous mixer, as is well known in the rubberprocessing industry. Layers or calendared sheets of stock are then readyto be built up in layered form with textile reinforcement and the like,the green reinforced rubber in sleeve or other form is vulcanized orcured under heat and pressure. If cured in sleeve form, individual beltsmay be cut from the sleeve. Typical synthetic rubbers useful in theinvention include polychloroprene, copolymers of ethylene and propylene,terpolymers of ethylene, propylene and diene monomers such as EPDM,styrene butadiene rubber, HNBR, CSM, silicone rubber, fluoroelastomers,mixtures of the foregoing, and alloys or mixtures of the foregoing orother known solid-processable rubbers mixed with suitable thermoplasticor thermosetting polymers or “plastomers”, polyethylene, polyester(e.g., Hytrel trademark) or materials such as Santoprene (Monsantotrademark). Liquid processable elastomeric materials such as thoseformed by liquid casting, applicable to many forms of polyurethane, arenot within this definition and are not contemplated by the embodimentsof the invention disclosed herein.

The belt of FIG. 10 is a four-ribbed serpentine belt employing a cord 20as disclosed herein, which is embedded in the rubber body of the belt.The cord members 20 may be any of the hybrid cords discussed above orbelow. The undercord section 159 of the belt may be formed of anunloaded rubber stock; however, typically it is formed of a suitablerubber in which has been mixed loading of discrete reinforcement fibers161 of desired material such as cotton, polyester or aramid. Themultiple ribs of the undercord section shown at 160, 162, 164, 166 maybe formed by grinding away the fiber loaded rubber between adjacentribs, up to the apex 163 between adjacent ribs, or by molding, flycutting or other suitable techniques. The shape and configuration of theribs is normally substantially matched to the corresponding shape of thepulleys 152 and 154 about which the belt is linked in drivingrelationship.

The overcord section of the belt shown at 165 includes a generally flatexterior belt back surface 153, a textile overcord material 155positioned at the exterior belt back surface, and an interposed rubberlayer such as adhesion gum layer 157 which is selected to adhere to thetextile material 155 as well as the adjoining cords 20. The adhesion gumlayer 157 may be formed of the same or similar (compatible) rubbermaterial as utilized in the undercord section 159 to ensure properadhesion and integration into the composite belt structure.

A method of forming the belt of FIG. 10 will be discussed in relation tothe apparatus of FIG. 9. On to a building drum 168 is first applied,optionally, an elongated transfer label 169 upon which is imprinted anydesired indicia, e.g., product numbers, trademarks, country of origin,to be imparted to back surface 153 of the belt. This transfer labeltypically is a relatively thin film of Mylar or other plastic materialbearing heat or pressure sensitive ink printing which duringvulcanization is transferred from the Mylar backing to the back surface153 of the belt. As the belt is built inverted, the next layer appliedon the drum is back surface 153 which includes a layer 167 of textilematerial 155 applied as a sheet over the mandrel 168 as mandrel 168rotates. Although it has been found satisfactory to employ a singletextile layer 167, obviously depending on the application, two or morelayers could advantageously be used, with any intervening rubber layerapplied as dictated by the application.

Over the layer 167 of textile material 155 is wrapped one or more layersof a rubber (e.g., elastomer) such as adhesion gum rubber 157.Preferably the ends of the layer(s) are butt spliced to avoid a lapwhich might otherwise be reflected as a protrusion or bump in the outersurface 153 of the belt. This gum layer 157 may alternatively be fiberloaded with any suitable reinforcement fiber such as cotton, polyesteror aramid, or may itself include one or more textile reinforcing layersembedded therein. Onto gum layer 157 is applied, by helically winding,strain-resisting tensile cord 20 in typical fashion. The tensile cordmay be closely or widely spaced, as needed, and an appropriate amount ofwinding tension is used, with the ends 20 a secured, as shown. Lastly,layer 161 which serves as the undercord of the belt, is wrapped over thehelically wound cord 20. This material may be gum stock, or includediscrete fiber loading 166 to enhance the modulus of the ribs 160, 162,164, 166.

Once the sleeve has been built up on drum 168, the assembly may beplaced inside a vulcanizing bag with steam pressure introduced to pressthe bag radially inwardly against the outer surface of the sleeve(against layer 161), consolidating and vulcanizing the sleeve incustomary manner. The mold may then be disassembled and the sleevedemolded. The sleeve may then be placed on a grinding drum and theprofile of ribs 160, 162, 164, 166 formed with complimentary shapedgrinding wheels or flycutters, removing undercord material between theribs, and up to apices 163. Alternatively, the ribbed profile may beformed by using a matrix airbag during vulcanization on drum 168, wherethe shape of the airbag is impressed into the overcord section 161.Alternatively, an airbag can be placed over mandrel 170 and the sleevepressed outwardly during vulcanization against a rigid outer shellmember having the conjugate shape of ribs 160, 162, 164, 166 formed inthe shell. Various methods of manufacture will be appreciated by thosehaving skill in this art.

With similar modifications the belt of FIG. 10 could also be builtupright, rather than inverted. In that case the outermost layer is thetextile layer with a further exterior layer of gum rubber thereover.

Exemplary belts were made using the cords of Examples 1-3 using themethod described above. These exemplary belts are 95.25 inches inlength, which length is simply an example. The belts had the followingcharacteristics: “A” section wrapped molded belts with a polychloroprenecore.

Belt Testing Methods Belt Flex Fatigue Life

Flex Fatigue Life, or simply Flex Life is a measurement of belt life ina situation where the belts flex and fail by flexing and is measured onan hour meter on a belt testing device, shown schematically in FIG. 5.Flex Fatigue Life is measured in hours and is determined using a deadweight type of test with a dead weight of 170 pounds and driven at 3300revolutions per minute (RPM). The elements of FIG. 4 are intentionallymisaligned as follows: (a) there is an eighth of an inch (⅛″)misalignment between the drive axle DR and the dead weight pulley DN and(b) there is a half-inch (½″) misalignment between the drive axle DR andthe slack idlers SL and tight idlers T, and (c) there is a five-eighthsinch (⅝″) misalignment between the idlers IDL and the dead weight pulleyDN. This misalignment has the effect of stressing the tensile cordunevenly and accelerating the tensile failure. The belt is set up andrun in this configuration until is breaks (complete failure). The periodof time from the start of the test until the belt breaks is the FlexFatigue Life for that belt.

Belt CD Growth

CD Growth is a measurement of the increase in length of a belt as aresult of the Flex Fatigue Life test. This is measured by recording theCenter Distance change of the belts on a test stand prior to tensilefailure. CD Growth is expressed as either an increase in absolute length(e.g., in inches) or as a percentage.

Belt Tensile Strength

Belt Tensile Strength is measured on an Instron® or MTS® Tensile testerusing flat pulleys.

Belt Test Results

The exemplary belts discussed above were tested using the test methodsdescribed above. The results are set forth below in Table 6, below,along with the same data for two other belts made with two non-hybridcords. The belt with the “Control 100% Aramid” cord was made as followsand has the following characteristics: “A” section wrapped molded V-Beltusing a polychloroprene core. The “(2000 denier Polyester, 1500 denierAramid)×3 Blended” cord was made by twisting a 2000 denier polyesteryarn and a 1500 denier aramid yarn together in a first twisting process.Three of these plies were then twisted in the opposite direction in thefinal twisting process. This blended cord contrasts with the wrappedcore concept of the hybrid cords disclosed herein. The belt with the“(2000 denier Polyester, 1500 denier Aramid)×3 Blended” cord was made asfollows and has the following characteristics: “A” section wrappedmolded V-Belt using a polychloroprene core.

TABLE 6 Flex Life CD Growth CD Growth Test Results-Dead Weight Flex Test(hr) (in.) (%) Control 100% Aramid 25 0.09 0.19% Hybrid-4000 denierPolyester Core, 90 0.34 0.71% 6 × 1500 denier Aramid Wrap Hybrid-2000denier Polyester Core, 60 0.19 0.40% 5 × 1500 denier Aramid Wrap (2000denier Polyester, 1500 94 0.45 0.94% denier Aramid) × 3 Blended

As can be seen, the two “hybrid” belts made with hybrid cords inaccordance with the disclosure herein had significantly longer Flex Lifethan the belt made with the “Control 100% Aramid” cord with less CDGrowth than the belt made with the “(2000 denier Polyester, 1500 denierAramid)×3 Blended” cord.

A significant number (about 34) of the belts made with the Example 3(ES1549) cords were tested in snowmobiles along with the same number ofaramid control belts. The control belts were made with the 100% aramidcords (Aramid 1500×2×3) discussed above in the Cord Heat Treatmentsection. As can be seen in FIG. 12, the belts made with the hybrid cordsshowed lower tensile strength degradation during field testing than the100% aramid cords during harsh testing in snowmobiles. Morespecifically, the data shown in FIG. 12 indicates that the endless powertransmission belts had an average tensile strength degradation of lessthan 12% after 23 hours of normal use in a snow mobile (e.g., not doinglong hill climbs for most of that time). Similarly, as seen in FIG. 13,the belts made with the hybrid cords showed higher displacement orelongation at break after field testing than the 100% aramid cordsduring harsh testing in snowmobiles (using a CD length of 46.0 in./2).As can be seen, the belts with the hybrid cords had higher retainedtensile strength and elongation at break than the belts with the aramidcords. More specifically, the data shown in FIG. 13 shows that theendless power transmission belts had an average displacement degradationof less than 8% after 23 hours of normal use in a snow mobile.

While the present invention has been illustrated by the description ofembodiments thereof, and while the embodiments have been described insome detail, it is not the intention of the applicant to restrict or inany way limit the scope of the appended claims to such detail.Additional advantages and modifications will readily appear to thoseskilled in the art. For example, lower numbers of higher moduluswrapping yarns may be employed than the maximum number and some of thebenefits from the invention might still be shown. In addition, the twistof a twisted cord can be determined by untwisting the final cord anduntwisting the individual wrapping yarns. After the final twist isremoved by untwisting the final cord one can measure yarn lengths of thewrapping yarn(s) and the core yarn(s). Additionally, cords can beremoved from V-belts and other elastomeric structures. Since the coreyarns may be thermoplastic and may have been stretched or otherwisedeformed during the cord heat treatment, one may detect no yarn lengthdifference in such a construction. In that case one can allow the cordto shrink without tension back to an initial configuration in an ovenheated to a temperature greater than the glass transition temperature ofthe core yarn for a period of at least five minutes. One could thenmeasure twist of the oven-exposed cord and measure the length differenceof the wrapping yarn(s) and the core yarn(s). The steps of methodsherein may generally be performed in any order, unless the contextdictates that specific steps be performed in a specific order.Therefore, the invention in its broader aspects is not limited to thespecific details, representative apparatus and methods, and illustrativeexamples shown and described. Accordingly, departures may be made fromsuch details without departing from the spirit or scope of theapplicant's general inventive concept.

What is claimed is:
 1. A method of making a heat-treated hybrid cord,comprising: providing at least one core yarn having a Young's modulus;and providing a plurality of wrapping yarns, each wrapping yarn having astrength of at least 2.5 GPa and a Young's modulus that is at least 5GPa greater than the Young's modulus of the at least one core yarn; andpre-twisting the wrapping yarns in a first direction with a twistmultiplier in the range of about 2 to about 6½; and twisting thepre-twisted wrapping yarns and the core yarn in the opposite directionwith a twist multiplier in the range of about 2 to about 6½ to form agreige hybrid cord; and then heat-treating the greige hybrid cord for atime at a temperature and under a load sufficient to accomplish any oneof or both of: (a) provide a free shrinkage of at least 2½ percent;and/or (b) provide a shrinkage force of at least 3 pounds; and whereinthe wrapping yarns in the greige hybrid cord have an untwisted yarnlength that is about 0.8% to about 5% greater than the untwisted yarnlength of the at last one core yarn in the hybrid cord.
 2. The method ofmaking a heat-treated hybrid cord according to claim 1 wherein twistingthe wrapping yarns in a first direction comprises twisting the wrappingyarns with a twist multiplier in the range of about 3 to about 4 andfurther wherein twisting the pre-twisted wrapping yarns and the coreyarn comprises twisting the pre-twisted wrapping yarns and the core yarnin the opposite direction with a twist multiplier in the range of about5 to about 6½.
 3. The method of making a heat-treated hybrid cordaccording to claim 1 wherein heat-treating the greige hybrid cordcomprises heating the greige hybrid cord under a load in the range ofabout 0.1 to about 3 grams per denier tension at a temperature in therange of about 100° C. to about 230° C. for a time in the range of about25 seconds to about 150 seconds in an oven for a time at a temperatureand under a load sufficient to accomplish any two or more of: (a)provide a free shrinkage of at least 4 percent; and/or (b) provide ashrinkage force of at least 4 pounds; and/or (c) provide an increase ofat least 50% in LASE3 value in the heat-treated hybrid cord as comparedto the greige hybrid cord; and/or (d) reduce the elongation at breakpercentage of the heat-treated hybrid cord by at least 1% as compared tothe elongation at break percentage of the greige hybrid cord.
 4. Themethod of making a heat-treated hybrid cord according to claim 1 whereinthe core contains a plurality of core yarns.
 5. The method of making aheat-treated hybrid cord according to claim 1 wherein the number of coreand wrapping yarns comprise one of (a) two core yarns and five wrappingyarns, (b) four core yarns and six wrapping yarns, and (c) three coreyarns and six wrapping yarns.
 6. The method of making a heat-treatedhybrid cord according to claim 1 wherein the number of wrapping yarns isequal to one of (a) the maximum integer number of those wrapping yarnsthat can be wrapped in a single layer around that core and (b) one lessthan the maximum integer number of those wrapping yarns that can bewrapped in a single layer around that core, as determined by theformula:Max Wrap Yarns=|cos β·π/α| where β=tan⁻¹(π·T·2·[r_(w)+r_(c)])α=sin⁻¹(r_(w)/[r_(w)+r_(c)]) T=twists per inch r_(c)=radius of core yarnr_(w)=radius of wrapping yarn.
 7. The method of making a heat-treatedhybrid cord according to claim 1 wherein each of the wrapping yarns hasa radius within the range of about 0.008 inches to about 0.015 inches, aYoung's modulus greater than 70 GPa, and a strength of at least 2.5 GPa.8. The method of making a heat-treated hybrid cord according to claim 1wherein the at least one core yarn has a radius within the range ofabout 0.010 inches to about 0.017 inches and a Young's modulus of 5.0 to70.0 GPa.
 9. The method of making a heat-treated hybrid cord accordingto claim 1 wherein each of the wrapping yarns has a radius within therange of about 0.008 inches to about 0.015 inches, a Young's modulusgreater than 70 GPa, and a strength of at least 2.5 GPa and wherein theat least one core yarn has a radius within the range of about 0.010inches to about 0.017 inches and a Young's modulus of 5.0 to 70.0 GPa.10. The method of making a heat-treated hybrid cord according to claim 1wherein the heat-treated hybrid cord has a breaking strength of at least320 pounds and a LASE3 value of at least 190 pounds.
 11. The method ofmaking a heat-treated hybrid cord according to claim 1 wherein the heattreatment provides a free shrinkage in the heat-treated hybrid cord ofat least 4 percent.
 12. The method of making a heat-treated hybrid cordaccording to claim 1 wherein the heat treatment provides a freeshrinkage in the heat-treated hybrid cord of 2%-4.3%.
 13. The method ofmaking a heat-treated hybrid cord according to claim 1 wherein the heattreatment provides a shrinkage force in the heat-treated hybrid cord ofat least 4 pounds.
 14. The method of making a heat-treated hybrid cordaccording to claim 1 wherein the heat treatment provides a shrinkageforce in the heat-treated hybrid cord of 3-16 pounds.
 15. The method ofmaking a heat-treated hybrid cord according to claim 1 wherein the heattreatment is done in three zones and in the third zone a load is appliedto provide the shrinkage force in the heat-treated hybrid cord of 3-16pounds.
 16. The method of making a heat-treated hybrid cord according toclaim 1 wherein the heat treatment is done in three zones, in the firstzone curing of epoxy or isocyanate adhesive takes place, and in thethird zone a load is applied to provide the shrinkage force in theheat-treated hybrid cord of 3-16 pounds.
 17. The method of making aheat-treated hybrid cord according to claim 1 wherein the heat treatmentprovides an increase of at least 100% in LASE3 value in the heat-treatedhybrid cord as compared to the greige hybrid cord.
 18. The method ofmaking a heat-treated hybrid cord according to claim 1 wherein the heattreatment provides an increase of at least 190% in LASE3 value in theheat-treated hybrid cord as compared to the greige hybrid cord.
 19. Themethod of making a heat-treated hybrid cord according to claim 1 whereinthe heat treatment provides an increase of 50%-190% in LASE3 value inthe heat-treated hybrid cord as compared to the greige hybrid cord andan elongation at break of less than 10%.
 20. The method of making aheat-treated hybrid cord according to claim 1 wherein: the number ofcore and wrapping yarns comprise one of (a) two core yarns and fivewrapping yarns, (b) four core yarns and six wrapping yarns, and (c)three core yarns and six wrapping yarns; each of the wrapping yarns hasa radius within the range of about 0.008 inches to about 0.015 inches, aYoung's modulus greater than 70 GPa, and a strength of at least 2.5 GPa;the at least one core yarn has a radius within the range of about 0.010inches to about 0.017 inches and a Young's modulus of 5.0 to 70.0 GPa;the heat treatment provides a free shrinkage in the heat-treated hybridcord of 2%-4.3%; the heat treatment provides a shrinkage force in theheat-treated hybrid cord of 3-16 pounds; and the heat treatment providesan increase of 50%-190% in LASE3 value in the heat-treated hybrid cordas compared to the greige hybrid cord and an elongation at break of lessthan 10%.